Wow. Awesome Thread. One note that I haven't seen (sorry if I'm just blind) is that reality is imperfect. Skin has flaws - scars, pores, uneven tans, moles. Also, people aren't built symetrically. Adding imperfection to a figure can add realism. For example, use a magnet to bend the tip of the nose... Lighting is obviously critical. So are the textures. But other elements, small elements like skin imperfections or an imperfect body, can all add to the realism.

Before they made me they broke the mold!
http://home.roadrunner.com/~kflach/